The present invention relates to a dosing system for combustion analyzers and particularly to a method and apparatus for correcting for nonlinearities in the display of the concentration of specimen gases.
In analyzers for the analysis of, for example, carbon and sulfur content in steel, absorption infrared cells are employed. As the concentration of the gases representing the carbon and sulfur content (CO.sub.2 and SO.sub.2 respectively) increase; the output signals from the infrared detectors vary in a non-linear fashion. Due to the fact that narrow band pass filters are employed, the output signals from the detectors do not follow the predictable logarithmic Beer's law curve for concentration. Accordingly, in order to provide reproducible and accurate readouts of detected concentrations of CO.sub.2 and SO.sub.2 representative of the carbon and sulfur content respectively of an unknown specimen; it is necessary to linearize the electrical signals from the detectors.
In the past with flow through type analyzers such as model CS-44, commercially available from Leco Corporation of St. Joseph, Mich., an electrical analog multiplier circuit was employed to provide a second order approximation in an effort to correct linearity. The circuit operates to provide a linear output signal to a point and then begins multiplying the input signal by a continually increasing value. This provided a linearity of approximately five percent which although an improvement over uncorrected systems, did not provide accuracy capable of achievement by the system of the present invention.